1. Field of the Invention
The present invention relates to a method for operating a chemical deposition chamber. In particular, the present invention relates to a method for operating a chemical deposition chamber so that a precursor fluid can be substantially stably guided into the chemical deposition chamber.
2. Description of the Prior Art
The method of chemical vapor deposition plays an important role in the manufacturing of the semiconductors. The chemical vapor deposition enables the construction and development of a solid film from various specific materials on a wafer, such as poly-Si layers, interlayer dielectrics, interlayer metal dielectrics, shallow trench isolations and passivations in a range from as low as 0.5 μm to several μm. The desirous elements or material layers are therefore formed on the wafers with the help of appropriate lithographic or etching procedures.
The general chemical vapor deposition system usually includes several parts, such as a deposition chamber, a wafer transfer device, a wafer supporting device and a precursor inlet. A substrate, such as a wafer, enters the deposition chamber and stays on the wafer supporting device through the wafer transfer device. The precursor fluid later enters the deposition chamber through the precursor inlet. Then the materials coming from the gas containing the atoms to be deposited are uniformly deposited on the substrate through chemical reactions.
There are many factors which are able to affect the quality of the chemical deposition, for example, the pressure of the deposition chamber, the temperature of the substrate, the flow rate of the gas, the path of the gas passing over the wafers, the chemical composition of the gas, the flow ratio among different gases, the reactions of the intermediates in the chemical reactions, whether the desirous reactions depending on exterior energy to accelerate or to induce themselves, the energy source outside of the deposition chamber such as the energy of the plasma, ion energy or the RF bias on the substrate. Further, the variables in the deposited films, such as the uniformity, step coverage on the patterns, chemical formulae (chemical compositions and distribution), crystallization orientation and defect density should be considered. Moreover, the deposition rate of the film is another factor, because it affects the throughput of the deposition chamber and a high deposition rate often compromise with the quality of the films.
In addition, the materials from the precursors by chemical reactions not only uniformly deposit on the substrate but also accumulate on the inner walls of the chemical deposition chamber to cause contamination along with by-products. Such materials and by-products accumulated on the inner walls of the chemical deposition chamber on one hand cause the source of contaminations such as particles or peelings, but also affect the thermal conductivity of the chemical deposition chamber. It is crucial how many times and how thorough the in-situ plasma cleaning are conducted on the chemical deposition chamber. In order to solve the problems, conventionally a pre-cleaning step is carried out on the chemical deposition chamber after a determined RF power hour, a determined number of processed chips and a determined time period to remove excess material layers.
For example, U.S. application 2005/0221020 provides a plasma enhanced chemical vapor deposition (PECVD) system. The method includes performing a chamber-seasoning step, which includes at least one of a deposition chamber cleaning step and a deposition chamber pre-coating step. After the deposition step, a post-process chamber cleaning process may be performed.
After the chamber-cleaning step, the precursor fluid will surely re-enter the chemical deposition chamber through the precursor inlet when the system is back on the deposition step on the wafers. However, the inventor observed that such precursor fluid re-entering the chemical deposition chamber would be under the situation of unstable flow rate, in particular at first re-entering the chemical deposition chamber. If a thinner film is about to be deposited on the substrate, the thickness of the film would be greatly fluctuating and the quality of the products would be therefore compromised.
One of the current solutions is that dummy wafers are used to test the deposition of the thickness of the films after the chamber-cleaning step to estimate the stability of the flow rate of the precursor fluid, or multiple dummy wafers are directly used to undergo the chemical deposition to drain the unstable flow of the precursor fluid during the dummy chemical deposition procedures. However, it is very complicated and time-consuming to transfer the dummy wafers into and out of the chemical deposition chamber through the wafer transfer device, to vacuum, to deposit the material layers and to measure the thickness of the material layers, which greatly influences the efficiency of the chemical deposition step.
Thus, there is a need for a novel method for operating a chemical deposition chamber to stabilize the flow rate of the precursor as soon as possible after the chamber-cleaning step to boost the efficiency of the chemical deposition step.